1. Field of the Invention
The invention relates to a liquid crystal display unit and a backlight module thereof; in particular, the invention relates to a liquid crystal display module with a thin backlight module.
2. Description of the Related Art
In a liquid crystal display unit of a liquid crystal display, a backlight module is generally utilized as a light source. In the backlight module, a prism plate is assembled with a light guide plate with a pattern design to attain a specified optical property.
FIG. 1a shows conventional assembly method of devices in the backlight module. In the conventional backlight module, optical films may be directly stacked, or adhered to each other by adhesive via separating blocks.
Specifically, in a frame 11 of the conventional backlight module 10, a reflector 12, a light guide plate 13, a diffuser 14, a prism plate 15, and a liquid crystal panel 16 are disposed as shown in FIG. 1a. A flexible printed circuit board 17, connected to the liquid crystal panel 16, is disposed outside the frame 11 and extends to the bottom of the reflector 12.
The conventional backlight module, however, has the following disadvantages.
The geometric shape of the conventional backlight module design is limited. Specifically, reduced thickness and brightness-enhancement of the prism plate are limited due to current manufacturing technology; hence, the thickness of the backlight module exceeds customer requirements, resulting in reduced demand.
An additional drawback of the conventional method is difficulty in positioning the prism plate. As shown in FIG. 1b, in the conventional backlight module, the prism plate 15 is formed with flanges 151 on both sides. It is noted that only one flange 151 is shown in FIG. 1b. The prism plate 15 can be positioned and fixed by means of the flanges 151, simplifying assembly thereof. When the prism plate 15 is deformed or rotated in a Z direction (as illustrated in FIG. 1b), however, there is large variation in brightness between different areas on the same side and lighter and darker pixel zones may occur.
The use of double-sided tape as separating blocks between devices complicates backlight module reworking required by low yield. The double-sided tape may also absorb and diffuse light, hence, the optical quality of the backlight module is unstable.
The prism plate is fixed in the conventional backlight module with flanges on each side. The flanges, however, are not symmetrically positioned, and as a result, the conventional backlight module is subject to thermal and residual stress after temperature testing. Thus, a stripe defect may be generated during operation of the backlight module. The use of flanges further complicates assembly and hinders automatic or semi-automatic mass production of the backlight module.
The flexible printed circuit board 17 is provided with a plurality of electronic devices 171. Thus, the thickness of the entire liquid crystal display unit may be increased due to the higher devices 171.